Combined heat and power system

ABSTRACT

A combined heat and power (CPH) system for a building has an electrical generator (12) For supply power and a gas engine (14) which drives the generator, contained in a housing (30). Recirculating air is drawn in through an inlet (32), over the electric generator, gas engine and its cooling and exhaust systems (38, 36) where it is heated by waste heat. It is then mixed with controlled amounts of fresh air to regulate the air temperature before being passed into the building air recirculating system. The gas engine can be run at a constant speed which is not dependent on the required temperature of the recirculating air.

The present invention relates to a combined heat and power system forgenerating electrical power and heat for a building.

A conventional low pressure hot water (LPHW) combined heat and powersystem comprises a gas engine driving an electric generator whichprovides a portion of the power required by a building. Waste heat fromthe combustion process in the engine is collected from the enginecooling system and exhaust system and transferred to a low pressure hotwater system by way of separate heat exchangers. The LPHW is pumpedaround the building to provide hot water for radiators, domestic hotwater systems and possibly to air handling unit heating coils. Such asystem is used in, for example, leisure centres and swimming baths,hotels, hospitals and sheltered housing.

However, one of the disadvantages of a conventional combined heat andpower system is the difficulty of recovery of waste heat from the engineand generator surfaces which prevents the efficiency of the systemrising above about 80%.

The present invention seeks to provide an improved system for providingelectrical power and heating for a building.

Accordingly, the present invention provides a system for providingelectrical power and heating for a building, comprising:

a housing having an air inlet and first outlet for connection to aventilation air system of the building and wherein the housing contains:

an electrical generator for generating electrical power; power drivemeans for driving said generator;

means for drawing recirculating air from said housing first inlet tosaid housing air outlet past said electrical generator and drive meanswhereby said air is heated by waste heat from said generator and saiddrive means;

wherein said housing has a second inlet downstream of said drive meansfor inlet of external air and said adjusting means comprising means formixing said recirculating air with said external air to adjust thetemperature of recirculating air passed to said first outlet; and

wherein said housing has a second outlet downstream of said drive meansfor exhausting recirculating air to atmosphere, and said mixing meanscomprises exhaust damper means for controlling the passage ofrecirculating air through said second outlet.

and adjusting means downstream of said drive means for adjusting thetemperature of said air;

and wherein said housing has a second inlet downstream of said drivemeans for inlet of external air and said adjusting means comprisingmeans for mixing said recirculating air with said external air to adjustthe temperature of recirculating air passed to said first outlet.

The phrase "external air" as used herein refers to air which does notform part of the recirculating air.

The term "gas engine" as used herein refers to any suitable type ofengine, e.g. internal combustion engine or gas turbine engine.

In a preferred embodiment of the invention the drive means has a coolingsystem including a heat exchanger for transferring heat from the coolingsystem to air flowing from the housing inlet to the outlet. The engineis a gas engine and has a further heat exchanger in an exhaust gassystem of the engine for transferring heat from exhaust gases of theengine to air passing from said housing inlet to said outlet. It will beappreciated that the heat exchangers may be placed in parallel withreference to the air flow or in series and may be provided withrespective air bypass arrangements to allow the flow of air partially orcompletely to bypass either one or both of the heat exchangers.

To further extract heat from the exhaust gas, the path of the exhaustsystem may be routed back through the engine/generator housing whereadditional extended surface heat exchangers may be installed.

The present invention is further described hereinafter, by way ofexample, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a conventional low pressure hot watercombined heat and power system; and

FIG. 2 is a schematic diagram of a preferred form of combined heat andpower system according to the present invention.

Referring firstly to FIG. 1 a conventional LPHW combined heat and powersystem 10 has an electric generator 12 which is driven by a gas engine14 to provide electrical power for a building such as a hospital orleisure centre. The gas engine 14 has an oil lubricating system 16 whichincludes an oil cooler heat exchanger 18 (sometimes omitted) whichtransfers heat from the oil to a fluid, normally water, circulatingaround a closed circuit 20. The gas engine also has a cooling system 22in which the coolant, normally water, is passed through a heat exchanger24 to transfer heat to the water circulating in the circuit 20.

Exhaust gas from the gas engine is also passed through a further heatexchanger 26 to transfer heat from the exhaust gas to the circulatingwater in the circuit 20.

Finally, heat from the circulating water in the circuit 20 is passed toa low pressure hot water system through a further heat exchanger 28.Several variants of this type of system exist, but in each, all of therecovered heat is transferred to water as the transport medium.

The known system of FIG. 1 suffers from several disadvantages. The gasengine output must be varied in order to take account of variations inelectricity and hot water requirements and has a thermal efficiency ofabout 80% with a considerable wastage of hot air.

Referring now to FIG. 2, this shows a preferred form of combined heatand power system for a building according to the present invention. Inthis system the gas engine 14 and the electrical generator 12 areenclosed in a housing 30 in a compartment 31 at one end thereof. Thehousing has a recirculating air inlet 32 adjacent the gas engine 14through which recirculating air from the building ventilation air systemis drawn by an extractor fan 34. The fan 34 is mounted in the housing ina position to draw air from the air inlet 32, around the generator 12and gas engine 14, over a heat exchanger 36 in an exhaust gas line ofthe gas engine 14 and also over a heat exchanger 38 in the coolingsystem of the engine in order to transfer waste heat from these to thecirculating air. The compartment 31 also has a cooling air inlet 33 witha controlling damper 39 which can be adjusted to allow varying amountsof cool, fresh air (external air) into the compartment 31 to mix withthe recirculating air drawn in through the air inlet 32. This providesan efficient way of introducing the statutory requirement of fresh airinto the ventilation system during the heating season. It also serves toincrease the efficiency of heat recovery from the engine and generatorsurfaces. The inlet damper 39 also enables the temperature of air drawnby the extractor fan 34 to be varied and allows the cooling effect ofthe circulating air on the gas engine 14 and the generator 12 to bevaried.

The air from the extractor fan 34 is then passed through a mixing box 40in the housing 30. The mixing box 40 has a recirculation air damper 42extending across the air flow path to control the amount of air flowingfrom the extractor fan to an air filter and supply fan downstream of theair damper 42. An exhaust outlet 47 with a controlling air damper 48 isprovided in the housing 30 between the extractor fan 34 and therecirculation air damper to control the amount of circulating air whichis exhausted to atmosphere whilst a fresh air inlet 49 and controllingdamper 50 is provided downstream of the recirculation air damper 42 tocontrol the amount of fresh, external air which is allowed into thehousing to mix with warm air from the extractor fan 34. This providescontrol over the temperature of the circulating air.

The dampers 42, 48 and 50 are controlled by one or more temperaturesensors which monitor the temperature of the circulating air in thebuilding.

The air thus passing through the air filter 44 and any other componentsof an air conditioning system (not shown) which may be present is thenpassed through an outlet 60 to circulation ducts in the buildingventilation air system by a supply fan 46 to provide heating during thecooler part of the year.

The preferred form of the invention uses fewer component parts andprovides a more compact installation than the known system and thereforehas a lower equipment cost. The potential total thermal efficiency ofthe system is 95% or higher, and exceeds that of the known LPHW systemby 10%-15%. In the system of FIG. 2 the gas engine 14 can be runcontinuously at its optimum running conditions with any excess heatgenerated being dumped to atmosphere through the exhaust air damper 48.This avoids the need to vary the operating output of the gas engine asin the known system of FIG. 1.

A further heat exchanger 70 can also be incorporated in the system toprovide hot water for a low pressure hot water system for the building.This can be effected by providing a low pressure water inlet 72 andoutlet 74 in the housing interconnected by the heat exchanger which isalso connected in the cooling system of the engine. This low pressurehot water may be used as domestic hot water or for heat transfer inanother air system. Alternatively, the cooling water in the coolingsystem can be used direct.

What is claimed is:
 1. A system for providing electrical power andheating for a building, comprising:a housing having a first inlet and anair outlet for connection to a ventilation air system of the buildingand wherein the housing contains: an electrical generator for generatingelectrical power; power drive means for driving said generator; meansfor drawing recirculating air from said first inlet to said air outletpast said electrical generator and drive means whereby the recirculatingair is heated by waste heat from said generator and said drive means;and adjusting means downstream of said drive means for adjusting thetemperature of the recirculating air; wherein said housing has a secondinlet downstream of said drive means for inlet of external air and saidadjusting means comprises mixing means for mixing the recirculating airwith the external air to adjust the temperature of the recirculating airpassed to said air outlet; and wherein said housing has a second outletdownstream of said drive means for exhausting the recirculating air toan external atmosphere, and said mixing means comprises exhaust dampermeans for controlling the passage of the recirculating air through saidsecond outlet.
 2. A system according to claim 1, wherein said mixingmeans comprises second inlet damper means for controlling the passage ofthe external air through said second inlet.
 3. A system according toclaim 2, wherein said second outlet is upstream of said second inlet andsaid mixing means further comprises a recirculation damper means betweensaid second outlet and said second inlet for controlling the flow of therecirculating air passing said second inlet.
 4. A system according toclaim 3, wherein said adjusting means further comprises means formonitoring the temperature of the recirculating air external of saidhousing and controlling said damper means in dependence thereon.
 5. Asystem according to claim 4, wherein said housing has a third inlet forinlet of the external air upstream of said drive means.
 6. A systemaccording to claim 5, wherein the system further comprises third inletdamper means for controlling the passage of the external air throughsaid third inlet.
 7. A system according to claim 6, wherein said drivemeans is a gas engine having a cooling system and an exhaust gas system.8. A system according to claim 7, wherein the system further comprisesfirst heat exchanger means in at least one of said cooling system andsaid exhaust gas system for transferring heat therefrom to therecirculating air.
 9. A system according to claim 8, wherein saidhousing further comprises:a fourth inlet and a third outlet forconnection to a low pressure hot water system of the buildings; and asecond heat exchanger means interconnecting said fourth inlet and saidthird outlet for transferring waste heat from said drive means to saidlow pressure hot water system.
 10. A system according to claim 9,wherein said second heat exchanger means is connected in said coolingsystem of said gas engine.
 11. A system according to claim 1, whereinsaid adjusting means further comprises means for monitoring thetemperature of the recirculating air external of said housing andcontrolling said damper means in dependence thereon.
 12. A systemaccording to claim 7, wherein the system further comprises third inletdamper means for controlling the passage of the external air throughsaid third inlet.